1. Field of the Invention
The present invention relates to a liquid ejection head that is able to eject a liquid from ejection ports and a method for manufacturing the liquid ejection head.
2. Description of the Related Art
Side shooter liquid ejection heads are known as common liquid ejection heads. The side shooter liquid ejection head has an energy generating element that allows droplets to be ejected perpendicularly to a surface of the head on which the energy generating element is located.
A side shooter liquid ejection head has been proposed which has an electric control circuit built into a substrate to drive the energy generating element. In the liquid ejection head, the electric control circuit is formed inside the substrate using a semiconductor manufacturing technique. A method for manufacturing such a side shooter ink jet head has been disclosed in Japanese Patent Laid-Open No. 09-011479 (1997). According to the method for manufacturing a side shooter ink jet head, disclosed in Japanese Patent Laid-Open No. 09-011479 (1997), the head is manufactured as follows. A substrate formed of silicon is provided, and a silicon anisotropic etching technique is used to form a liquid supply port in the silicon substrate. An ejection port forming layer is then joined to the silicon substrate. A liquid ejection head is thus manufactured.
FIGS. 12, 13A, and 13B show another method for manufacturing a side shooter liquid ejection head. According to the method for manufacturing the side shooter liquid ejection head, at first a liquid supply port formed in the silicon substrate is separated from a liquid channel formed in the ejection port forming layer by a layer formed of a thermal oxide film, an interlayer insulating film, and a protective film. In this state, the layer formed of the thermal oxide film, interlayer insulating film, and protective film is removed, by etching, from an area I shown in FIG. 12 forming the liquid supply port. This allows the liquid supply port to communicate with the liquid channel.
This type of liquid ejection head has been demanded to stabilize frequency properties in order to improve print quality in association with high-speed printing. To stabilize the frequency properties, it is necessary to stabilize a liquid refilling capability with which a liquid is supplied to the liquid channel between the energy generating element and the ejection port after droplets have been ejected from the liquid ejection head. In recent years, in order to improve image quality, the size of droplets has been reduced to increase printing density. Thus, in particular, the refilling capability has been demanded to be stabilized. The liquid refilling capability depends on the opening width of the liquid supply port as well as the distance from the opening end of the liquid supply port to the energy generating element.
However, when the liquid ejection head is manufactured in accordance with the method for manufacturing the ink jet head in Japanese Patent Laid-Open No. 09-011479 (1997), the liquid supply port is formed in the silicon substrate by etching. Consequently, the positional accuracy for the liquid supply port depends on the processing accuracy of the etching. However, for the etching of the silicon substrate, etching rate varies depending on the dissolvability of silicon with respect to an etchant. The dissolvability of the silicon substrate with respect to the etchant varies depending on the position on the silicon substrate. Furthermore, the silicon substrate may contain crystal defects or impurities. Consequently, the etching rate of the silicon substrate varies depending on the position on the silicon substrate. Thus, the positional accuracy of the opening end of the liquid supply port is not fixed; the opening end is not stably formed at the same position. Since the position of the opening end of the liquid supply port is not fixed, a part of the liquid supply port which is in communication with the liquid channel does not have a fixed opening width. Furthermore, the distance from the opening end of the liquid supply port to the energy generating element is not fixed. This prevents droplets ejected from the ejection ports from being stably supplied to print media. Thus, since the liquid supply port is formed in the silicon substrate by etching, a variation occurs in the accuracy of the opening width of the liquid supply port and in the accuracy of the distance from the opening end of the liquid supply port to the energy generating element.
According to the method for manufacturing the liquid ejection head shown in FIGS. 12, 13A, and 13B, the opening in that part of the liquid supply port which is in communication with the liquid channel is also formed by etching. Consequently, with this method, the processing accuracy of the opening width of the liquid supply port also depends on the processing accuracy of the etching of the liquid supply port, as is the case with the method for manufacturing the liquid ejection head in Japanese Patent Laid-Open No. 09-11479. Thus, the positional accuracy of the opening end of the liquid supply port in the manufactured liquid ejection head is not fixed; the opening end is not stably formed at the same position. The distance from the center of the energy generating element to the opening end of the liquid supply port is denoted by E in FIG. 13A and by F in FIG. 13B. As shown in FIGS. 13A and 13B, the distance from the opening end of the liquid supply port, formed by etching, to the energy generating element varies between E and F; the variation amounts to about 10 to 30 μm. This is due to a variation in silicon dissolvability and in the rate of the etching of the silicon substrate, depending on the area to be etched.